The present invention relates to an image recording method and an apparatus therefor, for example, to an image recording method and an apparatus therefor for recording an image by using a recording head which discharges ink.
Hitherto, in an apparatus for reproducing a binary image by a digital processing, such as a copying machine, a printer, a facsimile or the like, the collapse of dots becomes excessive in highlight portions and a marked granular appearance of the dots cannot be avoided when an image such as a photograph, a print or a picture in which dark and light gradients are finely expressed is recorded.
However, the conventional image processing technology cannot sufficiently overcome the above-described problems. Accordingly, a dark/light multi-valued recording method in which both dark and light ink are employed in a liquid jetting recording apparatus (a so-called ink jet printer) has been disclosed in U.S. Pat. No. 4,672,432.
According to this dark/light multi-valued recording method, the gradient in the highlight portion can be improved, the granular appearance of the dots can be reduced and the image quality can thereby be improved simply by replacing the binary processing with trinary processing. The reason for this is that applying low density ink to the highlight portion can remove the noise due to a sole dot.
Each of the output signal levels after separation by a dark/light separation table is supplied to a binary circuit in which it is converted into an on/off recording signal. The binary circuits are arranged to have the same structure for both dark and light ink.
However, in the above-described recording method depending upon the dark/light multi-valued processing, there has been a limitation to quintriple value processing due to the quantity of ink to be applied. Furthermore, since the dots for the dark ink and light ink are arranged to have the same diameter and the same binary circuits are provided in the apparatus, the excessive granular appearance of the dots of the dark ink cannot be prevented if dark ink is applied to a region printed with light ink in the highlight portion.
Furthermore, in a color recording apparatus employing four color components C (cyan), M (magenta), Y (yellow) and K (black), the granular appearance of K and M cannot be prevented. In particular, the skin color region such as the face of a person displays an excessive granular appearance due to the masking and UCR (Under Color Removal) conditions in the image processing. The problems of the type described above also arise in the other types of recording apparatus in which toner or donor film for a thermal printer is employed.